Make the build system respect CFLAGS

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -244,16 +244,6 @@
 endif()
 
 # flags
-# @TODO: set -Wall
-# @NOTE: -O3 is enabled in Release mode (CMAKE_BUILD_TYPE="Release")
-
-# Set the "-msse2" build flag only if the CMAKE_C_FLAGS is not already set.
-# Probably "-msse2" should be appended to CMAKE_C_FLAGS_RELEASE.
-if(CMAKE_C_COMPILER_ID STREQUAL GNU OR CMAKE_C_COMPILER_ID STREQUAL Clang OR CMAKE_C_COMPILER_ID STREQUAL Intel)
-     if(NOT CMAKE_C_FLAGS AND COMPILER_SUPPORT_SSE2)
-         set(CMAKE_C_FLAGS -msse2 CACHE STRING "C flags." FORCE)
-     endif(NOT CMAKE_C_FLAGS AND COMPILER_SUPPORT_SSE2)
-endif(CMAKE_C_COMPILER_ID STREQUAL GNU OR CMAKE_C_COMPILER_ID STREQUAL Clang OR CMAKE_C_COMPILER_ID STREQUAL Intel)
 
 if(MSVC)
     if(NOT CMAKE_C_FLAGS)